If you’ve ever made a candle that looks perfect on the outside but has a mysterious dip or hole in the middle once it cools, you’ve encountered the classic sinkhole problem. Don’t worry — this is one of the most common issues in candle making and is easy to troubleshoot once you understand what causes it.
What Are Sinkholes?
A sinkhole is a cavity or depression that forms in the top or centre of a candle as it cools. They often appear around the wick and can be shallow or deep, sometimes even extending down through the core of the candle.
While they might look unsightly, sinkholes are usually a natural result of the wax cooling and contracting — not a sign that your candle formula is wrong.
Why Do Sinkholes Happen?
Sinkholes occur because wax expands when melted and contracts as it cools. Here are the most common reasons they form:
- Rapid Cooling
If your candle cools too quickly, the outer edges solidify before the center does, trapping air pockets that later collapse into sinkholes. - Pouring Temperature Issues
Pouring wax that’s too hot or too cool can both lead to sinkholes.- Too hot = uneven cooling and cracking.
- Too cool = trapped air bubbles and poor adhesion.
- Container or Mold Shape
Deep or narrow containers retain heat differently from shallow ones, affecting how evenly the candle cools. - Wax Type and Additives
Some waxes (like soy) shrink more than others as they set, making them more prone to sinkholes. Additives like stearic acid can also change cooling behaviour
How to Fix Sinkholes
Even the most experienced chandlers deal with sinkholes from time to time — and they’re easy to fix!
1. Do a Second Pour
After the candle cools and you spot a sinkhole:
- Reheat a small amount of wax (5–10°C hotter than your first pour).
- Pour it carefully into the hole until it’s level with the surface.
- Allow it to cool slowly for a smooth, even finish.
2. Use a Heat Gun
For small surface dips, simply:
- Gently warm the top of the candle with a heat gun.
- Allow the wax to melt just enough to level itself out.
3. Tap and Test
When pouring, lightly tap or swirl your container to release any trapped air bubbles before the wax starts to set.
4. Control Your Cooling Environment
Cool your candles at room temperature (around 20–25°C), away from drafts, fans, or open windows. Consistent, gentle cooling helps prevent uneven shrinkage.
Pro Tip: Wick Centering Matters
Sinkholes often form right around the wick because that’s the last place the wax cools.
Using a wick centring tool or wick bar ensures even cooling and prevents wax from pulling away around the wick tab.
Sinkholes might look like a flaw, but they’re a normal part of the learning curve in candle making. With the right pouring temperature, patience during cooling, and a little troubleshooting know-how, you’ll achieve beautifully smooth tops every time.